The orb ponderer's arena first-person shooter

Shoot and survive

Open Source voxel shooter

Dhewm 3 is a Doom 3 GPL source port

Epic story-driven FPS running on the Build Engine

Game engine for Classic Doom

Leading the way in newschool multiplayer Doom online

Open source first person shooter

FPS aim trainer

Aliens vs Humans, First Person Shooter game with elements of Real Time Strategy

ReC98 source port of the first Seihou Project game

The Free and Fast Arena Shooter

Tank digging battle game

A modern cross‑platform port of “STAR WARS™: Dark Forces” with mod support

a modern QuakeWorld client focused on competitive online play

Modern cross-platform port of the Descent engine

Free fast paced arena shooter

Classic arena first person shooter

Game engine for Return to Castle Wolfenstein

First-person shooter with cooperative in-game map editing

A Zandronum 3.0 fork with improved netcode, configurable movement and many small tweaks

A modernization effort of DOOM-3-BFG

Source port for Build engine games

Fast paced, first person strategy game

Top-down shooter action RPG

First-person shooter game

Yamagi Quake II is an alternative client for id Software's Quake II

EDuke32 is an awesome, free homebrew game engine

Open source first person shooter

A Quake mod based on the retro shooter SPRAWL